1. Field of the Invention
The present invention relates to a scanner apparatus, more particularly to a scanner apparatus using an integration amplifying detector as a detector.
2. Description of the Related Art
As a means for detecting light of low luminance with high sensitivity, a means using an integration amplifier has been available. This integration amplifying detection means is designed to accumulate output charges by the integration amplifier, which have been subjected to photoelectric conversion by a photomultiplier tube (PMT) or a photodiode, convert the charges into voltages and then read them out.
Conventionally, such an integration amplifying detector has mainly been used for performing one-point observation in a time-sequential manner. In recent years, however, in order to observe a sheet-form object to be measured, which emits weak light, an application of the integration amplifying detector to a scanner for performing two-dimensional scanning has been tried.
The scanner using the integration amplifying detector generates a scanning position detecting clock indicating a period of information acquisition according to a scanning speed during main scanning, generates a timing pulse by using the scanning position detecting clock as a reference, and then indicates, to the integration amplifying detector, a period for executing integration, i.e., a measuring period, or a resetting period for releasing charges accumulated in the integration amplifying detector by this timing pulse.
The use of the scanner employing such an integration amplifying detector is advantageous, for example, for detection of photostimulating light in a radiation image recording/reproducing system (Japanese Unexamined Patent Publication No. 55 (1980)-12429 or the like) presented by an applicant of the present invention. This system uses an stimulable phosphor (photostimulable phosphor), which accumulates a part of radiation energy when irradiated with radioactive rays (X rays, xcex1 rays, xcex2 rays, xcex3 rays, electron beams, ultraviolet rays or the like) , and then shows phosphorescence according to the accumulated energy when irradiated with excitation light such as visible light. By using the stimulable phosphor, the system temporarily photographs and records the radiation image of an object, e.g., a human body, in the sheet-form stimulable phosphor, generates phosphorescent light by scanning the stimulable phosphor sheet with excitation light such as a laser beam, obtains an image signal by photoelectrically reading the generated phosphorescent light, and displays the radiation image of the object on a CRT based on the image signal by using an image recording/reproducing device or outputs the radiation image as a visible image on a photosensitive film.
In addition, to increase the readout speed (throughput) of the scanner apparatus using the above-described integration amplifying detector, bidirectional scanning should be desirably performed, which enables information to be detected in both going and returning ways, when a detection unit is scanned in a main scanning direction.
However, when bidirectional scanning is carried out by the scanner using the integration amplifying detector of the foregoing principle, a difference is generated in the integration starting time of the integration amplifying detector for obtaining information regarding each pixel between the going and returning ways of the scanner, causing a pixel positional deviation in the scanning direction between the going and returning ways. Consequently, jitters occur in the main scanning direction.
The present invention was made with the foregoing problems in mind, and it is an object of the invention to provide a scanner apparatus for performing bidirectional scanning by using integration amplifying detector, which is capable of eliminating jitters like those described above.
In accordance with the invention, a scanner apparatus having a bidirectional scanning function capable of scanning in both going and returning ways is provided. This scanner apparatus comprises: an integration amplifying detector for accumulating a detected quantity of light in a measuring period Ti within one cycle Tp, and releasing an accumulated quantity of light in a resetting period Tr; a scanning position detecting clock generator for generating a scanning position detecting clock of an interval equal to the cycle Tp for obtaining information by the integration amplifying detector; a timing pulse generator for deciding a resetting period Tr and a measuring period Ti of the integration amplifying detector based on the scanning position detecting clock, and generating timing pulses indicating the resetting period Tr and the measuring period Ti; and an A/D converter for converting a value of the quantity of light accumulated in the integration amplifying detector into a digital value. In this case, the timing pulse generator generates, in the returning way, the timing pulses by delaying a difference period Td generated between the going and returning ways.
In the scanner apparatus of the invention, the bidirectional scanning function capable of scanning in both going and returning ways is not limited to one where an object to be scanned is mechanically reciprocated, but includes one where a scanning optical system is reciprocated with respect to a fixed object to be scanned.
According to the scanner apparatus of the invention, the scanning position detecting clock generator may change the cycle Tp of the scanning position detecting clock according to a measuring condition.
The measuring condition means one for a resolution priority mode designed to enhance resolution by reducing sensitivity, or for a sensitivity priority mode designed to enhance sensitivity by reducing resolution.
According to the scanner apparatus of the invention, the timing pulse generator may generate the timing pulses to set a positive value for the difference period Td, detect the scanning position detecting clock with detection accuracy variance of 1% or lower, or generate the timing pulses to set a measuring period Ti longer by four times or more than a resetting period Tr. Moreover, when no scanning position detecting clock is detected in a cycle longer by 1.5 times than the cycle Tp for obtaining the information, the timing pulse generator may generate a timing pulse indicating a resetting period Tr.
Now, a method for calculating the difference period Td will be described by referring to FIG. 2 showing a time relation between a scanning position detecting clock and a timing pulse.
In the drawing, a scanning direction 1 indicates the going way of a main scanning direction; a scanning direction 2 the returning way of the main scanning direction; Tp the cycle of the scanning position detecting clock; Tw the pulse width of the scanning position detecting clock; Tr the resetting period of the integrator of the integration amplifying detector; Ti the integrating period of the integration amplifying detector; and Td a difference period between the going and returning ways when the information of the same place is obtained in the main scanning direction.
The cycles Tp and the pulse widths Tw of the scanning position detecting clock are equal between the going and returning ways, and pulse generation positions are identical with respect to the position of main scanning.
In the scanning direction 1, i.e., the going way of the detection unit, to detect an n-th pixel from the left, the timing pulse generator generates a pulse indicating resetting for the period Tr from the rising edge by using the rising edge of an n-th pulse of the scanning position detecting clock as a reference, and a pulse indicating measuring for the period Ti after the passage of time Tr from the rising edge.
In the scanning direction 2, i.e., in the returning way of the detection unit, to detect a position substantially identical to an n-th place detected in the going way in the main scanning direction, the timing pulse generator generates a pulse indicating resetting for the period Tr from the rising edge by using the rising edge of the n+1st pulse from the left of the scanning position detecting clock as a reference, and a pulse indicating measuring for the period Ti after the passage of time Tr from the rising edge.
In this case, if the center of the measuring period Ti is set as a measuring position, then the center position of the measuring period Ti is shifted by the difference period Td between the going and returning ways.
The difference period Td is calculated by an equation (1) below. Since a difference is within one pixel, it is impossible to make corrections by moving positions left and right by pixel units for every main scanning line after the detection of information, causing jitters in this difference period Td.
Td=Tpxc3x97Twxe2x88x92(2xc3x97Tr+Ti)xe2x80x83xe2x80x83(1)
Thus, in the returning way, a timing pulse is generated by delaying an amount equal to the difference period Td, thus preventing the center shifting of the measuring period Ti between the going and returning ways.
With the scanner apparatus of the invention constructed in the foregoing manner, by changing the measuring timing of the integration amplifying detector between the going and returning ways, the center of the measuring period Ti can be prevented from being shifted for every main scanning line. As a result, it is possible to prevent the occurrence of jitters.